Bottom sediments collected in the Northwest (NW) Pacific Ocean in 1997 were analysed for 90 Sr, 137 Cs, 239,240 Pu and 241 Am contents to determine their distribution patterns, inventories and sources. Enhanced inventories of 239,240 Pu and 241 Am were observed in the latitudinal belts of 10-208N and 30-408N, which correspond to major areas of local (tropospheric) and global (stratospheric) fallout (with a contribution from local fallout), respectively. The sediment inventory of 239,240 Pu near the Bikini Atoll exceeded its overlying water inventory, however, in the mid-latitudes, more than 70% of 239,240 Pu still remains in the water column. 241 Am inventories in sediments exceeded that of the water column for the entire NW Pacific Ocean. Higher 137 Cs and 90 Sr sediment inventories in the latitudinal belt of 30-408N are due to global fallout, and they account for about 10% and less than 5% of the water column inventories, respectively. The observed activity ratios of 137 Cs/ 90 Sr, 238 Pu/ 239,240 Pu and 241 Am/ 239,240 Pu in sediment were at some stations higher than the global fallout ratios due to contributions from local fallout and due to specific processes in the water column. Two end-member mixing model based on the 240 Pu/ 239 Pu atom ratios observed in global and local fallout yielded ~60% contribution of the local fallout in the bottom sediments near the Bikini Atoll. The upward decrease in the 240 Pu/ 239 Pu atom ratios in the sediment column indicates a decrease in the contribution of local fallout to the Pu inventory with time. 241 Am and 241 Pu dating of sediment layers was utilized to explain a hiatus in sediment accumulation in the deep seafloor.